1. Field of the Invention
The present invention relates to a process and apparatus for manufacturing a semiconductor thin film such as silicon thin film.
2. Description of Related Art
In a process for manufacturing a semiconductor, a technology for forming semiconductor thin films is an important factor since the formed thin films constitute a semiconductor device structure so that they give a great influence upon the characteristics, yield and reliability of the device.
The thin film forming technology is mainly classified into CVD (chemical vapor deposition), PVD (plasma vapor deposition), applying and coating process and plating process. The former CVD and PVD are mainly used. CVD and PVD processes are classified into various many processes.
For example, vacuum deposition, plasma CVD, evacuated or normal pressure CVD, reactive sputtering, ion plating, optical CVD processes are conducted for forming amorphous silicon films. Plasma CVD process is mainly used for this purpose.
The largest problem resides in that it is difficult for prior art to form uniform thin films having a large area. Since the uniformity of the film tissue structure and film thickness is related with various manufacturing factors. It is very difficult to control them.
Therefore, it is an object of the present invention to form a semiconductor thin film which is excellent in uniformity of the film tissue structure and the film thickness by supplying a substrate having a thin film formed on the surface thereof with hydrogen radicals to effect the tunnel reaction while the substrate is cooled to temperatures below 40 K.
The present invention provides a process for forming a semiconductor thin film on the surface of a substrate by supplying said substrate with hydrogen radicals under cryogenic condition below 40 K, preferably below 20 K, more preferably 10 K.
When the substrate having a thin film on the surface thereof is cooled, heat is removed from the support which supports the substrate through heat conduction via a cooling head of a refrigerator.
In this case, a hydrogen radical gas discharge opening is provided so that it faces the thin film on the substrate. It is preferable to uniformly supply hydrogen radicals to the thin film surface from the hydrogen radical gas discharge opening.
The semiconductor thin film formed on the substrate may have lattice defects. The lattice defects can be repaired by conducting an annealing treatment. In this case, it is preferable to heat the substrate having the thin film formed thereon through heat conduction via the support so that the temperature of the substrate is elevated to temperatures above room temperature. Stabilization of the thin film can be achieved by supplying said thin film with hydrogen radicals at high temperatures.
Although annealing can be conducted in a separate chamber different from a thin film forming chamber, it is preferable to continue the supply of the hydrogen radicals in the course of heating substrate from the cryogenic temperatures such as 40 K to high temperatures above room temperature in the same chamber in order to prevent the introduction of foreign materials and to enhance the annealing effect.
In one aspect of the present invention, there is provided an apparatus for forming a semiconductor thin film, comprising a vacuum chamber, a refrigerator having a cooling head, hydrogen radical generating means, a support for supporting a substrate which is in contact with said cooling head, hydrogen radical generating means for generating hydrogen radicals by exciting a hydrogen-containing gas and a hydrogen radical gas discharge opening which is disposed opposite to said substrate for spraying a hydrogen-containing gas which contains hydrogen radicals generated from said hydrogen radical generating means upon said thin film.
In another aspect of the present invention, there is also provided an apparatus for forming a semiconductor thin film, comprising a vacuum chamber, a refrigerator having a cooling head, which is capable of cooling the head to temperatures below 40 K, hydrogen radical generating means, a support for supporting a substrate which is in contact with said cooling head so that it is cooled, heating means for heating said support to temperatures above room temperature, hydrogen radical generating means for generating hydrogen radicals by exciting a hydrogen-containing gas and a hydrogen radical gas discharge opening which is disposed opposite to said substrate for spraying a hydrogen-containing gas which contains hydrogen radicals generated from said hydrogen radical generating means upon said thin film.